1. Field of the Invention
This invention relates generally to communications systems, and, more particularly, to a communications device that uses intra-bundle signaling to negotiate with other communication devices.
2. Description of the Related Art
In communications systems, particularly telephony, it is common practice to transmit signals between a subscriber station and a central switching office via a two-wire, bi-directional communication channel. The Plain Old Telephone System (POTS), designed primarily for voice communication, provides an inadequate data transmission rate for many modern applications. To meet the demand for high-speed communications, designers have sought innovative and cost-effective solutions that take advantage of the existing network infrastructure. Several technological advancements that have been proposed in the telecommunications industry make use of the existing network of telephone wires. One of these technologies is the xDSL technology. DSL technology uses the existing network of telephone lines for broadband communications. An ordinary twisted pair equipped with DSL interfaces can transmit videos, television, and high-speed data.
DSL systems use digital signal processing (DSP) to increase throughput and signal quality through common copper telephone wire. Certain DSL systems provide a downstream data transfer rate from the DSL Point-of-Presence (POP) to the subscriber location at speeds of about 1.5 Megabits per second (MBPS). The transfer rate of 1.5 MBPS, for instance, is fifty times faster than a conventional 28.8 kilobits per second (KBPS) transfer rate.
One popular version of the DSL technology is the Asymmetrical Digital Subscriber Line (ADSL) technology. The ADSL standard is described in ANSI T1.413 Issue 2, entitled, xe2x80x9cInterface Between Networks and Customer Installationxe2x80x94Asymmetric Digital Subscriber Line (ADSL) Metallic Interface, the most recent revision of which as of the filing date of this specification is incorporated herein by reference in its entirety.
ADSL modems use two competing modulation schemes: discrete multi-tone (DMT) and carrierless amplitude/phase modulation (CAP). DMT is the standard adopted by the American National Standards Institute. The technology employed by DMT ADSL modems is termed discrete multi-tone. The standard defines 256 discrete tones. Each tone represents a carrier signal that can be modulated with a digital signal for transmitting data. The specific frequency for a given tone is 4.3125 kHz times the tone number. Tones 1-7 are reserved for voice band and guard band (i.e., tone 1 is the voice band and tones 2-7 are guard bands). Data is not transmitted near the voice band to allow for simultaneous voice and data transmission on a single line. The guard band helps isolate the voice band from the ADSL data bands. Typically, a splitter may be used to isolate any voice band signal from the data tones. Tones 8-32 are used to transmit data upstream (i.e., from the user), and tones 33-256 are used to transmit data downstream (i.e., to the user). Alternatively, all the data tones 8-256 may be used for downstream data, and upstream data present on tones 8-32 would be detected using echo cancellation. Because more tones are used for downstream communication than for upstream communication, the transfer is said to be asymmetric.
Through a training procedure, the modems on both sides of the connection sense and analyze which tones are less affected by impairments in the telephone line. Each tone that is accepted is used to carry information. Accordingly, the maximum capacity is set by the quality of the telephone connection. The maximum data rate defined by the ADSL specification, assuming all tones are used, is about 8 MBPS downstream and about 640 KBPS upstream.
In a typical ADSL system, a central office (CO) modem communicates with a customer premise (CP) modem over a subscriber line. The CP modem is typically installed in a home or office. The training process is conducted point-to-point (i.e., from the central office to the subscriber). The CO and CP modems negotiate based on the conditions of the subscriber line to maximize the capabilities of the communications link therebetween. The ability of the various tones that make up the ADSL spectrum to carry data depends on numerous factors, including distance from the central office and impairments resulting from noise, cross-talk, etc. Generally, higher tones are significantly attenuated on a long loop connection, and thus, are not useful for carrying data. As a result, the lower tones are used to carry the majority of the data. For shorter loop connections, both the lower and the higher tones may be used to increase throughput or decrease the error rate (e.g., by sending less bits per tone).
Recently, the number of disparate data transmission devices using the subscriber line as a communications channel has increased. For example, home network systems have been developed that use the preexisting internal phone wiring of the home as a network communications channel. The frequency bands used in such a home network commonly overlap those used by an ADSL modem. All wiring downstream of the central office is generally seen as a common bus. That is, the internal wiring of the house is essentially directly connected to the central office. Signal sources generated on the subscriber end have the potential to affect line conditions elsewhere, even out of the subscriber facility.
If a user wishes to implement both a home network and ADSL service, it is typically necessary to fine tune either or both of the services to prevent interference therebetween. For example, the tones used by the ADSL system may be changed or the power level of the ADSL modem or network may be raised or lowered to reduce interference. This type of fine-tuning is possible where the interfering systems are connected to the same subscriber and are presumably under the control of the same entity. However, it is possible for a device such as a modem or home network installed at one facility to deleteriously affect the operation of another such device at a different facility. In such a case, there is no common entity having the authority or means for fine-tuning the respective systems.
Typically, multiple subscriber lines (e.g., 50) exit the central office in a bundle. Individual subscriber lines (i.e., twisted pairs) exit the bundle at different points depending on their respective destinations. The signal present on a particular subscriber line may interfere with the signal on another adjacent subscriber line, a phenomenon known as cross-talk. Consider an ADSL modem on one subscriber line establishes a connection with the central office. The modem is on a relatively short loop and could use high or low tones, but, because the lower tones are more robust, the modem concentrates its bandwidth in the lower tones. At some later time, a second ADSL modem on a longer loop attempts to establish a connection. Because the loop is relatively long, the higher tones cannot be effectively used. Assume the two subscriber lines run close to each other in the bundle. The lower tone signals from the first modem increase the noise detected in the lower tones by the second modem. As a result, the second modem may have difficulty negotiating sufficient bandwidth to establish a connection at its rated data rate.
Such an interfering case may also occur between two home networks or a home network and a modem. The communications signal generated by a home network is not confined to the internal wiring of the installation site because the connection to the central office is continuous. Thus, the network signal is present on the subscriber line wiring within the bundle and may cause cross-talk interference with a home network or modem on an adjacent subscriber line.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.
One aspect of the present invention is seen in a communications system including first and second subscriber lines, a first device, and a second device. The first device has a first negotiation unit coupled to the first subscriber line. The second device has a second negotiation unit coupled to the second subscriber line. The first negotiation unit is adapted to send a first negotiation signal on the first subscriber line. The first negotiation signal induces through cross-talk a second negotiation signal on the second subscriber line. The second negotiation unit is adapted to modify an operating parameter of the second device based on the second negotiation signal.
Another aspect of the present invention is seen in a method for negotiating operating parameters in a communications system. A first negotiation signal is transmitted from a first device coupled to a first subscriber line. The first negotiation signal is received in a second device coupled to a second subscriber line independent of the first subscriber line. An operating parameter of the second device is modified based on the first negotiation signal.